Fluorescent imaging device

ABSTRACT

An imaging system for use with an endoscope, including a light source which emits white light and excitation light which will produce a fluorescence response by an object under inspection, an imaging camera including separate paths for processing images produced by white light and excitation light, a selection device that causes the imaging device to operate in a white light mode or an excitation light mode, and a protective device that prevents damage to high-sensitivity imaging components from exposure to excessive light input. Fluorescent image data are separated into at least red and green color bands which are separately processed to produced a video display in which normal tissue is displayed in predetermined specific color, and abnormal tissue in one or more distinctly different colors. In one embodiment, an image color interpretation guide is provided in the form of multiple color bars which are superimposed on a single video display device with the image display. of different kinds. In another embodiment, color control is provided by adjusting the amplification of the imaging components for each of the color bands while viewing tissue known to be normal using a recursive algorithm until the ratio of the maximum values of the color separation signals fall within a predetermined range. The high-sensitivity imaging components are protected by controlling impingement of light on the imagining components, selectively controlling emission of white and excitation light from the light source, and controlling the power source for the imaging components.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 09/153,793,filed Sep. 15, 1998 No. 6,422,994, issued Jul. 23, 2002 in the name ofMamoru KANEKO, Hitoshi UENO, Sakae TAKEHANA, Isami HIRAO, NobuyukiDOGUCHI, Takeshi OZAWA, Takefumi UESUGI, Katsuichi IMAIZUMI, YasukazuKOGEN, Makoto TOMIOKA, Tadashi HIRATA and Masahiro KAWAUCHI entitledFLUORESCENT IMAGING DEVICE.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluorescent imaging devices to conductfluorescent observations by using an endoscope to irradiate anexcitation light onto an area of a biological tissue to be examined withsuch devices being characterized by the ability to switch betweenfluorescent observation and a conventional reflected light observation.

2. Description of the Related Art

Recently, diagnostic techniques have been developed using an endoscopeto irradiate tissue to be studied with visible light and to detectresulting fluorescent images which are then analyzed for diagnosticpurposes. These techniques have been found particularly useful fordiagnosing disease conditions such as cancers or tissue degeneration andfor highlighting the boundary regions of the conditions under study.These techniques are sometimes enhanced by also studying normal lightimages resulting from reflection of the irradiating visible light(usually white light).

In the case of autofluorescence, i.e., the stimulated emission resultingfrom impingement of the excitation light onto a biological tissue, thefluorescence typically has a longer wavelength than that of theexcitation light. Fluorescent substances within organisms areexemplified by collagens, NADH (nicotinamide adenine dinucleotide), FMN(flavin mononucleotide), pyridine nucleotide and the like. Recently, therelationship between such fluorescent substances and various diseaseshas been recognized, making it possible to diagnose cancers and the likeby these fluorescences.

In addition, certain fluorescent substances such as HpD(hematoporphyrin), Photofrin, ALA (δ-amino levulinic acid), and GFP(Green fluorescent protein), have been found which are selectivelyabsorbed by cancers and thus may be used as contrast materials. Inaddition, certain fluorescent substances may be added to a monoclonalantibody whereby the fluorescent may be attached to affected areas by anantigen-antibody reaction.

As the excitation lights, for example, lasers, mercury lamps, metalhalide lamps and the like are used. For example, when a light with thewavelength of 437 nm is emitted onto a gastrointestinal tract tissue,green autofluorescence by abnormal tissues is attenuated compared to theautofluorescence of normal tissues, but red autofluorescence of abnormaltissues is not attenuated as much compared to the autofluorescence ofnormal tissues. A transendoscopic fluorescent observation deviceutilizing this principle to image the green and red fluorescentemission, and to show the existence of abnormal tissues has beendisclosed in Japanese Unexamined Patent Publication No. 9-327433.

Since the fluorescent images obtained in this way have very weakintensities compared to the reflected images obtained with conventionalwhite light, photomultiplication, for example, using an imageintensifier is necessary.

Generally, when a blue or ultraviolet light is emitted onto biologicaltissue, an autofluorescence occurs within a longer wavelength band thanthat of the excitation light. Moreover, fluorescent spectra aredifferent between normal tissues and abnormal tissues such asprecancerous tissues, cancerous tissues, inflammatory tissues, anddysplastic tissues so that the existence of lesions and conditions oflesions can be detected based on the changes in delicate coloration ofthe fluorescent images.

In particular, since with a blue excitation light, the intensitydistribution of fluorescence stimulated near the green region,especially that of 490 nm-560 nm, is stronger in normal tissue than indiseased tissue, emissions in the green region and in the red region,e.g., wavelengths in the 620 nm-800 nm region are arithmeticallyprocessed to generate two-dimensional fluorescent images, and by thesefluorescent images the discrimination between affected areas and normalareas can be achieved.

Video images are produced for diagnostic observation of theautofluorescent emissions, and adjustments are made to the ratio betweenthe video signals corresponding to the green and red fluorescentintensities to allow normal tissues to have a certain color tone.Accordingly, tissue known to be normal is first observed, and the ratiosof the red and green emissions are adjusted to establish a referencecolor tone. Then, after the adjustment of the color tone of the normalparts, the potentially diseased tissue is observed. In this way, thenormal parts are designated with a certain color tone and abnormal partsare designated with different color tones from that of the normal partsdue to the attenuation of the green signal. By the differences in colortones between abnormal and normal parts, the abnormal parts can bevisualized. Typically, the ratio is adjusted so that the normal tissueappears a cyanic color tone and diseased tissue appears a red colortone.

Moreover, in a fluorescent observation device of Japanese UnexaminedPatent Publication No. 8-557, a single light source is used both as anexcitation light to conduct fluorescent observations and as a whitelight to conduct white light observations by insertion and removal of afilter. Endoscopes usually also include an emergency light source whichpermits safe removal of the instrument in case of failure of the mainlight source.

As will be understood, when only fluorescent images are desired, thereshould be no illumination by white light, but only by the excitationlight. Thus, switching is required so that when a white light image isto be obtained, a white light is emitted, and when a fluorescent imageis to be obtained, an excitation light is emitted.

Also, switching is controlled so that, when white light is emitted, theresulting image is provided only to a white image imaging device, andwhen the excitation light is emitted, the fluorescent image is providedonly to the high-sensitivity fluorescent imaging device. However, withconventional fluorescent imaging devices, since the endoscope is out ofthe body when power is applied, if the device is accidently set in itsfluorescent observation mode, ambient light may impinge on thefluorescent imaging device. Then, an excess of light enters the imageintensifier, and overprint at the high-sensitivity imaging plane of theimage intensifier occurs, resulting in its breakdown.

Also with the fluorescent observation device of said Japanese UnexaminedPatent Publication No. 8-557, in the case of lamp failure duringfluorescent observation, the emergency light provides insufficientluminous energy to excite the tissue sufficiently, making it difficultto observe fluorescence. In addition, even with the emergency light, ifthe filter for excitation light generation is carelessly removed from infront of the emergency light, the image intensifier will be burnt.

Moreover, since the delicate variations in coloration of fluorescentimages are subjectively visualized by the operator, the lack of fixeddiscrimination standards makes it difficult to compare of findings bydifferent users, and at different facilities such as hospitals.

Also in the conventional example in Japanese Unexamined PatentPublication No. 9-327433, since adjustment of color tone for normalparts is performed on the individual judgment of the user, the absenceof fixed calibration standards renders objective diagnosis by color tonedifficult.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a fluorescent imagingdevice which protects a fluorescent image high-sensitivity imagingmeasure even under a transitional condition such as at the power input.

Another object of the present invention is to provide a fluorescentimaging device which prevents damage to the high-sensitivity camera ifthe normal emitting lamp fails during a fluorescent observation and isreplaced by the emergency light.

Still another object of the present invention is to provide afluorescent imaging device which objectively discriminates againstdelicate changes in coloration of fluorescent images so that an operatorcan easily visualize the existence of lesions and conditions of thelesions.

A further object of the present invention is to provide a fluorescentimaging device which adjusts the color tone of normal tissues to adesired tone by conducting a simple operation during the observation ofthe normal tissue, while displaying the color tone of abnormal tissue incontrast with the color tone of the normal tissues.

The fluorescent imaging device of the present invention has a lightsource, which selectively switches between an excitation light and awhite light, introduces the light into a light guide, and then emits thelight onto the tissue being inspected; a high-sensitivity fluorescentdevice for fluorescent images; a white image imaging device for whitelight images; a device which couples the fluorescent image to thefluorescent imaging device, a device which prevents overprint on thehigh-sensitivity imaging plane of the fluorescent imaging device, avisible image generation device which generates an electric signaloutput from the fluorescent imaging device, and a separate visible imagegeneration device which generates an electric signal output from thewhite light image imaging device.

BRIEF DESCRIPTION OF THE DRAWINGS

A first embodiment of the present invention is illustrated in drawingsFIGS. 1-4 where:

FIG. 1 is a structural schematic of an endoscopic fluorescent imagingdevice;

FIG. 2 is a front elevation which illustrates one structural example ofthe rotary filter;

FIG. 3 is an enlarged section of the structure around the movablemirror;

FIG. 4 is a table which illustrates the relationship between switchingconditions of each device and imaging conditions of the camera;

A second embodiment of the present invention is illustrated in drawingFIGS. 5-8 where:

FIG. 5 is a structural schematic of an endoscopic fluorescent imagingdevice;

FIG. 6 is a front elevation which illustrates structure of the rotaryfilter that is not illustrated in FIG. 5;

FIG. 7 is a front elevation which illustrates an RGB rotary filter;

FIG. 8 is a table which illustrates the relationship between switchingconditions of each device and shutter conditions of the camera;

A third embodiment of the present invention is illustrated in drawingFIGS. 9 and 10 where:

FIG. 9 is a front elevation of another rotary filter;

FIG. 10 is a structural schematic of the fluorescent observation device;

A fourth embodiment of the present invention is illustrated in drawingFIGS. 11-14 where:

FIG. 11 is a structural schematic of the fluorescent image device of thefourth embodiment;

FIG. 12 is a spectrum atlas of the fluorescences emitted from normal andabnormal tissues;

FIG. 13 is a color distribution diagram showing the relationship incoloration between the normal part and the lesion parts in fluorescentcolor observation images;

FIG. 14 is a schematic diagram that illustrates one structural exampleof the color index;

A fifth embodiment of the present invention is illustrated in drawingFIGS. 15-17 where:

FIG. 15 is a structural schematic of the structure of the fluorescentimage device of the fifth embodiment;

FIG. 16A is a histogram showing the frequency of the green image signallevel;

FIG. 16B is a histogram showing the frequency of the red image signallevel;

and

FIG. 17 is a flowchart which illustrates the operations to set normaltissues to a certain tone.

FIG. 18 is a schematic diagram of a sixth embodiment of the presentinvention.

FIG. 19 is a schematic diagram of a seventh embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention will now be described withparticular reference to FIGS. 1-4.

The fluorescent imaging device of this embodiment has an imaging cameraincluding a white light imaging device and a high-sensitivityfluorescent imaging device, a device to couple a power source to thecamera, and an overprinting prevention device to protect thehigh-sensitivity imaging plane by controlling a movable mirror on anoptical path so that under the imaging condition where the power sourceis ON, imaging by the fluorescent imaging device is prevented.

As shown in FIG. 1, the fluorescent imaging device 1 comprises anoptical endoscope 2 which is inserted into the body under examination, alight source 3 which supplies an illumination light to the endoscope 2,an imaging camera 4, including an integrated imaging device which can beremovably attached to the endoscope 2, a control center 5 which conductssignal conditioning for the imaging device in the camera 4, and amonitor 6 which provides a visible image for diagnostic observation.

A switch 7 on camera 4 is provided to operate a control circuit 8 incontrol center 5. Control circuit 8 controls the operation of lightsource 3 and camera 4 to provide the desired light source, to preventimpingement of white light on the fluorescent image detectors, and, bymeans of a switching arrangement 42, to provide either a signalrepresenting either the fluorescent image or the white light image tomonitor 6.

Endoscope 2 has a slender insertion part 11, an operation part 12 at theback end of the insertion part, an eyepiece part 13 at the back end ofthe operation part 12, and a light guide cable 14 which extends from theoperation part 12. A connector 15 removably couples light source 3 tothe end of light guide cable 14.

A light guide 16 which functions to conduct the incoming white light orexcitation light, is inserted in insertion part 11, operation part 12,and light guide cable 14. By installing connector 15 onto light sourcedevice 3, the white light or the excitation light is provided from thelight source device 3 to light guide 16.

As an illumination light source 2 such as a metal halide lamp or thelike is provided in light source device 3. The white light emitted fromthis lamp 21 passes through a rotary filter 23 which is rotated by astepping motor 22, and then is supplied to the light admittance end ofthe light guide 16 through a condensing lens 24.

As shown in FIG. 2, rotary filter 23 is disk shaped, and includes afirst circular aperture 25A and a second circular aperture 25B. A clearglass insert 25 may be provided in aperture 25A if desired. Secondaperture 25B is fitted with a blue filter 26 which passes the excitationlight with a wavelength in a narrow-band of the blue region, preferablyabout 400-450 nm. When aperture 25A is positioned in front of lightsource 21 white light is supplied into light guide 16, and when the bluefilter 26 is positioned in front of light source 21 (as shown in FIG.2), blue light for fluorescent observation is supplied into the lightguide 16.

The rotational position of the stepping motor 22 is controlled bycontrol circuit 8. Moreover, a small opening 27 is formed at thecircumference of rotary filter 23, and a photo coupler 28 is disposed sothat it spans across the circumference. When the photo coupler 28detects the hole 27, it provides a position detection signal indicatingthat the blue filter 26 is positioned on the optical path.

As shown in FIG. 1, photo coupler 28 includes a light source and a lightdetector (not shown) disposed on opposite sides of the rotary filter 23.When filter 26 is aligned with light source 21, hole 27 is positionedbetween the light source and the detector of photo coupler 28, allowinglight to pass through from the light source to the detector. The lightdetector is coupled to control circuit 8.

A power switch (not shown) is provided for light source 3. When thisswitch is turned ON, power is supplied to lamp 21 and to stepping motor22, which starts to rotate filter 23.

The light which is transferred by light guide 16 is emitted onto thetissue under examination, such as an organ of a body cavity, through theillumination lens 31 which provides an illumination window at the tippart 29 of the insertion part 11.

An objective lens 32 which provides an observation window is installednear to lens 31. This focuses an image, either reflected white light ora fluorescent image resulting from the excitation light, on an imageplane at the tip of the image guide 33. The image which is formed on thetip plane of image guide 33 is transferred onto the back end plane 33Aof the image guide 33. A magnified view of the image provided by lightguide 33 is available through an eyepiece lens 34 of an eyepiece part 13which is positioned adjacent to the back end plane of the image guide33. This image may be viewed by the naked eye when camera 4 is notattached to endoscope 2.

When the camera 4 is mounted onto the eyepiece part 13, theimage-forming lens 37 within the camera is disposed opposite to eyepiecelens 34.

On the resulting optical path, within camera 4, is a movable mirror 38,which is movable between the position shown in FIG. 1 and the position38A shown in outline. When it is in the position shown, light focused bylens 37 is reflected to impinge on a second fixed mirror 39, so that thelight which is reflected from movable mirror 38 is also reflected bymirror 39, to form an image on the imaging plane on a first chargecoupled device (CCD) 40 which services the white light imaging device.

The optical image which impinges on CCD 40 is converted to an electricalsignal and is coupled to a first camera control unit (CCU) 41. Thisconverts the input electrical signal into video signal for display onmonitor 6 through a switching arrangement 42 when the tissue is beingexamined under white illumination. Movable mirror 38 is driven by adriver controlled by control circuit 8. For the white light observationmode, mirror 38 is in the position shown in solid lines and the lightfocused by lenses 34 and 37 is coupled to white light image imagingdevice 40. For the fluorescent observation mode, a control signal sentfrom control part 8 to driver 43 causes movable mirror 38 to be set inthe position shown by dotted lines. Then, light which goes throughlenses 34 and 37 is coupled to fluorescent imaging device 44.

The position of movable mirror 38 is detected by a photoreflector 45. Asshown in FIG. 3, the luminous element 46 a and the light detector 46 bwhich form photoreflector 45 are disposed opposite to the plane of, forexample, the proximal end of movable mirror 38. Thus, when mirror 38 isin the position shown with the solid line, the output signal of lightdetector 46 b is provided as the second mode signal (see FIG. 1) tocontrol circuit 8.

Fluorescent imaging device 44 comprises a dichroic mirror 48 which isinclined at 45 degrees on the optical path. Dichroic mirror 48selectively reflects red light but transmits the rest of the visiblespectrum.

The light transmitted by dichroic mirror 48 then passes through a greenfilter 49 which selectively transmits the light with green wavelengthsto an image intensifier (I.I.) 50. The green light is amplified by I.I.50 to form an image on an imaging plane 51 of the CCU for fluorescenceuse 56.

The light which is reflected by dichroic mirror 48 is further reflectedat a mirror 52 and then, passes through a red filter 53 whichselectively transmits light with red wavelengths, to an I.I.54. The redlight then is amplified at I.I. 54 to form an image on the imaging plane55 of the CCU for fluorescent use 57.

The outputs of CCU 56 and 57 are converted into a video display signalby an image processing device 58. The video signal is coupled to monitor6 through the switching arrangement 42 described below.

Switching arrangement 42 is controlled by the control circuit 8 inconjunction with switch 7 which allows the operator to select a mode ofoperation, i.e., white light imaging, fluorescent imaging, orsimultaneous white light and fluorescent imaging.

As previously noted, power for camera 4 is supplied by control center 5.When the power is first turned ON, the control circuit 8 goes intooperation ahead of other parts. Specifically, the control circuit 8confirms that the power is present prior to operating a relay whichsupplies power to the other circuits.

Thereafter, control circuit 8 determines the position of movable mirror38 at its initial condition. If in error 38 is found to be in theposition shown by the solid lines and the camera 4 is not operation,control circuit 8 operates driver 43 to set mirror 43 in the positionshown by the dotted lines. In this way, even if a transitional conditionexists (e.g., if light source 3 is ON and filler 23 is set to emit whitelight, when the power source of the control center 5 is turned ON),white light will not impinge on fluorescent imaging device 44.

In addition, when the power for control center 5 is turned OFF, a shutdown operation is initiated on which driver 43 is disabled. This againprevents white light from impinging on the fluorescent imaging device 4.

Also, control circuit 8 monitors the ON/OFF condition of the power forlamp 21. When the power for light source 3 is turned ON, after a delayto allow the power source to reach a stable state, control circuit 8operates stepping motor 22 with reference to a feedback signal providedby photo coupler 28 and also operates movable mirror 38 through driver43. During the start-up delay, control circuit 8 retains mirror 38 inthe position shown by the solid lines. Thereafter stepping motor 22 anddriver 43 are operated to select the desired color for the lightsupplied by filter 23 and the optical path for light collected by imageguide 33, in accordance with the position of switch 7.

When the power for light source device 3 is turned OFF, the controlcircuit 8 immediately disables driver 43, which sets movable mirror 38into the position shown by the solid lines. This prevents admittance oflight to the fluorescent imaging device 44, and thereby prevents damageto I.I.s 50 and 54.

Now, the operation of this first embodiment will be explained.

The sequence of operation for camera 4 from the condition in which thepower for light source 3 and control center 5 are both OFF to thecondition in which both are turned ON is illustrated with reference toFIG. 4.

When the power for both light source 3 and control center 5 is OFF,neither the white light nor fluorescent light is emitted into the camera4, and operating power is not supplied to the imaging devices of camera4. Therefore, the camera 4 is in the “inoperative” condition as shown inFIG. 4.

When the power for light source 3 is turned ON, but the power forcontrol center 5 is still OFF, although the white light or thefluorescent light is ready to be emitted into the camera 4, operatingpower is not supplied to the imaging devices and camera 4 is still inthe “inoperative” condition as shown in FIG. 4.

If the power for light source 3 is OFF but the power for control center5 is turned ON, at first, neither reflected white light nor stimulatedfluorescent light is coupled to the camera 4. Nevertheless, sinceoperating power is supplied to both of the imaging devices, movablemirror 38 is set at the position shown by the solid lines, and thecamera 4 is set to operate in the “white light mode,” as indicated inFIG. 4.

If power is supplied to both light source device 3 and control center 5,during the start up delay, movable mirror 38 is set at the solid lineposition so that even through both of imaging devices are energized,camera 4 is still in “the white light mode.”

After the start-up delay, if white light imaging is selected by switch7, the control circuit 8 controls the rotation of the stepping motor 22and positions a clear glass insert 25 in the optical path of lamp 21,and confirms the position of filter 23 by detection of a signal fromphoto coupler 28. If the level of the detection signal indicates thatthe detector in photo coupler 28 is not energized, control circuit 8keeps the movable mirror at the solid line position.

Then, white light from lamp 21 is transmitted through clear glass insert25 in aperture 25 a of filter 23, and passes light guide 16 toillumination lens 31 to illuminate the tissue under examination.

The light which is reflected from the tissue under examination isfocused at the tip plane of the image guide 33 by the objective lens 32,is transferred onto the back end plane of the image guide 33, isreflected at the movable mirror 38 and is then imaged at the CCD forwhite use 40.

The output signal of this CCD for white use 40 undergoes signalconditioning at the CCU for white use 41 and is converted into a picturesignal, which is displayed as a white light image on the monitor 6through switching arrangement 42.

On the other hand, if the fluorescent imaging mode is selected by switch7, the control circuit 8 controls the rotation of the stepping motor 22and positions the blue filter 26 on the optical path, while confirmingthe position by the detection signal of the photo coupler 28. When thedetection signal indicates that the blue filter is in the properposition, control circuit 8 operates driver 43 to switch movable mirror38 to the dotted line position, thereby enabling the “fluorescent mode.”

With the blue filter in front of lamp 21, only light components withblue wavelengths are transmitted through light guide 16, to illuminatethe tissue under examination.

The fluorescence generated by the blue excitation light is focused ontothe tip plane of image guide 33 by objective lens 32, is transferredonto the back end plane of the image guide 33, and then impinges ondichroic mirror 48 within the camera 4. The light transmitted bydichroic mirror 48 passes through green filter 49, is amplified by I.I.50, and imaged at the CCD for fluorescence use 51.

On the other hand, the light reflected by dichroic mirror 48 is furtherreflected by mirror 52, passes through red filter 53, is amplified byI.I. 54 and is imaged at the CCD for fluorescence use 55.

The output signals of CCDs for fluorescent use 51 and 55 undergo signalconditioning at the CCUs for fluorescent use 56 and 57, respectively,and are converted into picture signals. Then, image processing such asadjustment of intensity of the images, image component registration andthe like is performed by image processing device 58, and, both imagesare superimposed with different colors and displayed as a fluorescentimage on the monitor 6 through the switching arrangement 42.

If combined white light and fluorescent imaging is selected by switch 7,the control circuit 8 rotates the stepping motor 22 at a constant speed.Then as shown in FIG. 2, when the detection signal of the photocoupler28 indicates that the blue filter 26 is disposed on the optical path,control circuit 8 operates driver 43 to switch the position of themovable mirror 38 from the solid line to the position to the dotted lineposition, and conducts the fluorescent imaging as described above, andthen stores the fluorescent image in a memory circuit (not shown) withinimage processing device 58.

When blue filter 26 is rotated away from lamp 21 by stepping motor 22,the control circuit 8 disables driver 43, and movable mirror 38 movesfrom the dotted line position to the solid line position to permit whitelight imaging. The resulting white light image is stored in a memorycircuit (not shown) in the CCU for white use 41.

Thereafter filter 23 rotates further, and clear glass 25 withdraws fromthe optical path. When the blue filter 26 is again positioned in theoptical path, as indicated by the detection signal of the photocoupler28, the control circuit 8 operates driver 43 to switch the position ofthe movable mirror 38 back to the dotted line position. In this way, themovable mirror 38 is switched into the fluorescent imaging condition andconducts the fluorescent imaging of the next frame, and then stores thefluorescent image in memory within the image processing device 58. Inthis way, both images of each frame, namely the white light image andthe fluorescent image are sequentially obtained and stored into thememory.

By operating switching arrangement 42 alternatively with appropriatetime intervals, control circuit 8 allows the white light image and thefluorescent images to be alternatively displayed on monitor 6.

Alternatively, by shifting the timing between reading the memory of theCCU for white use 41 and reading the memory of the image processingdevice 58, both images may be displayed simultaneously on monitor 6.

Thus, according to this embodiment, before a certain operation mode isset, such as during the start-up delay excessive light is prevented fromimpinging on fluorescent imaging device 44 to protect thehigh-sensitivity image plane from overprinting, with a consequentbreakdown of the I.I.s 50 and 54 caused by the admittance of excessivelight.

Even during a transitional condition of switching from the fluorescentimaging mode to the white light imaging mode, the imaging circuits areswitched before the condition of the light source device 3 is shiftedfrom the emitting of the excitation light to the radiation of the whitelight.

In addition, when switching from the white light imaging mode to thefluorescent imaging, the imaging circuits are switched after the lightsource 3 is switched from white light to the excitation light, so abreakdown of the I.I.s 50 and 54 caused by admittance of excessive lightinto the fluorescent imaging device 44 is prevented.

Although photocoupler 28 detects that the blue filter 26 is positionedon the optical path as shown in FIG. 2, a second photocoupler may beprovided to detect that the clear glass insert 25 is positioned on theoptical path. Thus, by detecting signals from these two photocouplers,the rotary operation of the stepping motor 22 and the operation of themovable mirror 38 can be controlled with greater certainty.

Moreover, although in this embodiment, where movable mirror 38 ispositioned on the optical path when the power source of control center 5is turned ON, the admittance of the light to the fluorescent imagingdevice 44 is prevented so that the damage to the I.I.s 50 and 54 thatwould be caused by the admittance of an excessive light or the like, isprevented. Also, the fluorescent imaging device 44 may be in thenon-imaging condition by controlling the operating power source to theI.I.s 50 and 54, to provide further protection.

For example, when the switch for the power source of the control center5 is turned to be ON, the control circuit 8 may detect the condition ofthe light source 3 so when light source 3 is turned ON, unless the bluefilter 26 is set on the optical path, as indicated by the output of thephotocoupler 28, operating power would not be supplied to the I.I.s 50and 54.

In this case, for example, when the power source for control center 5 isturned ON but the power for light source 3 is kept OFF, the non-imagingcondition is established, but even if the power for light source 3 isturned ON, only if the blue filter 26 is disposed on the optical path,is operating power supplied to the I.I.s 50 and 54.

Moreover, when rotary filter 23 is rotated to shift clear glass insert25 into position on the optical path, until it is actually positioned onthe optical path, as indicated by the detection signal from thephotocoupler 28, the non-imaging condition is not established where theoperating power source is supplied to the I.I.s 50 and 54. Byestablishing this non-imaging condition, the breakdown due to theexcessive admittance of the light into the I.I.s 50 and 54 can beprevented, which breakdown could possibly occur when the fluorescentimaging mode is still maintained during the switching operation. Whenswitching from the white imaging mode to the fluorescent imaging modecondition, the breakdown of the I.I.s 50 and 54 can similarly beprevented.

Instead of controlling the operation power source to the I.I.s 50 and54, by decreasing the sensitivities of the I.I.s 50 and 54, a conditionmay be set where even if light having an intensity that far exceeds thatof fluorescence enters the fluorescent imaging device 44, no overprintcan occur and breakdown is prevented.

In addition, provision may be made to control the light source 3 whichemits the excitation light and the white light to be the initialcondition where the excitation light is secured to be emitted when, forexample, the power source of the light source device is turned to be ON.In this way, even with a camera which is intended only for fluorescentimaging, and has no provision to protect the fluorescent imaging device44, damage which might result if the power for the camera is turned ONbefore the camera is set to the proper condition for use can beprevented.

The second embodiment of the present invention is illustrated withreference to FIGS. 5 to 8.

In this embodiment, the endoscope is an electronic endoscope whichintegrates a white light image imaging device at its tip, where afluorescent image introducing part of a fluorescent imaging device isinserted into a forceps channel of this electronic endoscope, afluorescent image which is introduced through his fluorescent imageintroducing part is imaged at the fluorescent imaging part, and then thesignals are processed in, for example, a CCU for fluorescent use withina control center so that a white light image and a fluorescent image areto be designated on a monitor.

As shown in FIG. 5, the fluorescent imaging device 61 of this embodimentis composed of an electronic endoscope 62, a light source 63, a CCU forwhite use 64, a fluorescent observation device 65, control center 66,and a monitor 67.

Unlike the endoscope 2 of FIG. 1, in electronic endoscope 62, the CCDfor white use 68 is disposed at the imaging position of the object lens32. Therefore, the electronic endoscope 62 does not have the image guide33 and the eyepiece part 13. Also, CCD for white use 68 in thisembodiment does not generate an image of reflected white light per se,but rather a synthesis of red, green and blue component color imageswithin the visible region, as an equivalent of a white light image.

The signal conductor 68 a connected to CCD for white use 68 passes frominsertion part 11 through a light guide cable 14, and is connected tothe CCU for white use 64 through an additional cable 64 a which isconnected to cable 68 a through a suitable 64 b.

Also, a forceps channel 71 is provided. A light tube 72 is positioned inforceps channel 71, as described in more detail below.

Light source device 63 includes a rotating filter 74 (FIG. 7) positionedon the optical path between rotary filter 23 and lamp 21. Rotary filter74 is driven by a motor 75.

As shown in FIG. 6, the structure of filter 23 is the same as that inFIG. 2, and the output signal from photocoupler 28 is provided to acontrol circuit 77 within a control center 66.

As shown in FIG. 7, filter 74 comprises a red filter component 76 R, agreen filter component 76 G, and a blue filter component 76 B asindicated by two-headed arrow 74 a, filter 74 and the motor 75 aremovably mounted so that filter 74 may be shifted out of the optical pathof lamp 21. A suitable driver mechanism 78 operated by control circuit74 is provided for this purpose.

Positioned within light tube 72 is an image guide 81. A lens 82 islocated at the back end of image guide 81. A lens 82 is opticallycoupled to an imaging lens 83. A movable shutter 84 is disposed front oflens 83. Control center 66 includes a control circuit 77.

Among the functions of control circuit 77 are to operate movable shutter84. In the position shown in FIG. 5 by solid lines, shutter 84 permitslight to pass from lens 83 to the dichroic mirror 48. In the positionindicated by the dotted lines, shutter 84 blocks light passing throughlens 83 from reaching mirror 48. Mirror 48 is part of fluorescentimaging device 44 which is the same as that included in the firstembodiment described in connection with FIG. 1.

The output signal of the CCDs 51 and 55 are provided to a common CCU forfluorescent use 85 within control center 66, which generates afluorescent picture signal. This signal is coupled by switchingarrangement 68 to a monitor 67. A picture signal from the CCU for whiteuse 64 is also coupled by switching arrangement 68 to monitor 67.

A switch 87 is provided on the camera 73 to select the mode ofoperation. Based on the selection made by switch 87, circuit 77 controlsthe operation of shutter 84, driver 78 and switching arrangement 86 asdescribed in more detail below. Control center 66 also providesoperating power to camera 73 and CCU for white use 64.

In the second embodiment, essentially the same control functions areprovided as in the first embodiment. For example, shutter 84 is normallyin a closed condition. When a driving signal is provided by controlcircuit 77, the shutter is moved to an open condition. In addition,control circuit 77 monitors the ON/OFF condition of the power for lightsource 63. When the power source is turned ON, circuit 77 maintainsshutter 84 in its closed condition during a start-up delay interval.When the power for light source 63 is turned OFF, circuit 77 immediatelyswitches shutter 84 into its closed condition. Further description ofthe structural features is omitted in the interest of brevity.

The operational states for this embodiment are illustrated withreference to FIG. 8.

When the power sources for light source 63 and control center 66 areboth OFF, the light source 63 does not generate a white light or anexcitation light, and since the driving signal is not applied by controlcircuit 77 to shutter 84, shutter 84 remains in the “closed” position,as indicated in FIG. 8.

When the power source of the light source 63 is OFF but the power sourcefor control center 66 is ON, at first, control circuit 77 keeps theshutter 84 in its closed condition. Therefore the shutter 84 is in the“closed” condition, as indicated in FIG. 8. Shutter 84 also remainsclosed during the start-up delay period when the power sources of boththe light source 63 and control center 66 are turned on.

After the start-up delay period, if the white light imaging mode isselected by operation of switch 87, the control circuit 77 controls therotation of the stepping motor 22 to position clear glass insert 25 onthe optical path for lamp 21 and confirms the position by means of thedetection signal of the photocoupler 28.

In response, the detection signal corresponding to the positioning ofclear insert 25 in the path of lamp 21 shutter remains in the “closed”condition. Also, the control circuit 77 control the drive mechanism 78to position the RGB rotary filter 74 on the optical path of lamp 21, andoperates monitor 75 to rotate filter 74. As a result, recurringsequences of red, green, and blue light pulses pass through clear glassinsert 25 of rotary filter 23 and are coupled to light guide 16 throughlens 24. The light pulses are emitted onto the tissue under examinationthrough the illumination lens 31. The light pulses which are reflectedfrom the illuminated tissue are imaged onto the CCD for white use 68 bymeans of the object lens 32 as previously described in connection withthe first embodiment.

The output signal from CCD for white use 68 undergoes signalconditioning at the CCU for white use 64 to convert it into a picturesignal which is then displayed on the monitor 67 through switchingarrangement 86.

When the fluorescent imaging mode is selected by means of switch 87, thecontrol circuit 77 controls drive mechanism 78 to shift motor 75 andfilter 74 out of the optical path of lamp 21, and operates steppingmotor 22 to position blue filter 26 in the optical path. The properpositioning of blue filter 26 is confirmed by the detection signal fromphotocoupler 28, as previously described. When the control circuit 77receives the detection signal indicating the blue filter 26 is properlypositioned, it drives shutter 84 to the “open,” position, as indicatedin FIG. 8.

With filter 26 in place, only light with the blue wavelength is suppliedinto the light guide 16, to provide the excitation light forilluminating the tissue under examination.

The fluorescence generated by the excitation light is imaged at the tipplane of the image guide 81 by the lens 82, and is transferred throughthe image guide 81, to dichroic mirror 48 within the camera 73. As thelight which is transmitted by dichroic mirror 48 passes through greenfilter 49 and then, after the light-amplification by the I.I. 50, isimaged with the CCD for fluorescent use 51.

On the other hand, the light which is reflected by the dichroic mirror48 is further reflected by mirror 52, and passes through red filter 53.After light-amplification by I.I. 54, the red light is imaged at the CCDfor fluorescent use 55.

The output signals of the CCDs for fluorescent use 51 and 55 undergosignal conditioning at the CCU for fluorescent use 85 and are convertedinto picture signals for display as fluorescent images on the monitor 67under control of switching arrangement 86.

If the operating mode is switched from fluorescent to white lightimaging, control circuit 77 first closes shutter 84, operates drivemechanism 78 to shift the RGB rotary filter 74 into operating positionin front of lamp 21, and operates monitor 22 to set the clear glassinsert 25 of the rotary filter 23 in the optical path of lamp 21.

Then, the RGB rotary filter 74 which is rotated by the motor 75, imagesthe white light image as described above and the white light image isdisplayed on monitor 67.

Thus, according to this embodiment, before an operation mode is set, forexample, during start-up, shutter 84 remains in its closed condition toprevent excessive light from being admitted to the fluorescent imagingdevice 44, with a consequent damage to the I.I.s 50 and 54.

When switching from fluorescent to white light imaging, shutter 84 isset to be closed before light source 63 is switched from emittingexcitation light to emitting of white light. Similarly, when switchingfrom white light to fluorescent imaging, shutter 84 is opened only afterlight source 63 is switched from emitting of white light to emitting ofexcitation blue light, again preventing admittance of an excessive lightinto the fluorescent imaging device 44.

A third embodiment of the present invention is illustrated in FIGS. 9and 10.

As shown in FIG. 9, the rotary filter 23 a differs from the rotaryfilter 23 of the first and second embodiments, in that an emergencylight 91 is also provided.

As shown in FIG. 10, light source 63 a is provided with rotary filter 23a and a burnt lamp detector 92. The latter detects if lamp 21 becomesinoperable, e.g., if it burns out, by monitoring the lamp output.

The detection signal from burnt lamp detector 92 is coupled to a controlcircuit 77 by a conductor 92 a. If the light output of lamp 21 fallsbelow a predetermined level as indicated by the signal on conductor 92a, control circuit 77 operates to active emergency light 91. Also, awarning device 93 is activated to warn an operator that the lamp 21 isinoperative.

In particular, if lamp 21 becomes inoperative during use, the burnt lampdetector signals control circuit 77 and warning device 93, which emits asignal by means of a buzzer, warning light or the like.

If this happens with the system in the fluorescent mode, control circuit77 responds to the detection signal on conductor 92 a to close shutter84 (see FIG. 10) so that light transmitted through imaging lens 83 doesnot impinge on dichroic mirror 48.

Next, the control circuit 77 drives motor 22 to rotate the rotary filter23 a so that the light from the emergency light 91 is introduced intolight guide 16. Then, once emergency light 91 is aligned with the lightadmittance end of light guide 16, control circuit 77 turns on emergencylight 91 to secure a field of view.

Emergency light 91 may be activated before or at the same time as motor22, as long as it is after shutter 84 has been closed. Alternatively,instead of closing shutter 84, the sensitivities of the I.I.s 50 and 54may be reduced.

On the other hand, if white light is being used, when lamp 21 becomesinoperative, the control circuit 77 responds to the detection signal onconductor 92 a to maintain shutter 84 in the closed position, and drivesmotor 22 to move rotary filter 23 a into a position such that light fromthe emergency light 91 may be coupled into light guide 16. Then, whenthe rotation of filter 23 a is completed, and emergency light 91 ispositioned properly, control circuit 77 activates emergency light 91.Alternatively, emergency lamp 91 may be activated while motor 22 isstill in motion.

Thus, in this third embodiment, whether lamp 21 becomes inoperativeduring the course of fluorescent observation or white light observation,the emergency light is not turned on until the image intensifiers havebeen protected.

In addition, since when the emergency light 91 is lighted, the bluefilter 26 of the rotary filter 23 a is always out of the optical path,sufficient illumination is provided for safe removal of endoscope 61.

Alternatively, in the third embodiment, provision may be for theoperator to activate the emergency lighting sequence described above,for example, by means of a switch or the like.

Moreover, emergency light 91 may be, for example, a light emitting diodewhich emits a light with a wavelength within the detection band of thefluorescent imaging device. Therefore, if the lamp 21 becomesinoperative in the course of a fluorescent observation, the rotaryfilter 23 a is rotated so that light from the light emitting diode iscoupled to the light guide 16. On the other hand, if the lamp 2 becomesinoperative in the course of a white light observation, the shutter 84which has been positioned to block the optical path of imaging lens 83may be opened while the rotary filter 23 a is being repositioned, afterwhich light form the light emitting diode is coupled to the light guide16.

In this way, imaging using the light emitting diode emergency lightsource may continue, and miniaturization, electric power-saving andreduction in costs of the illumination for emergency use can beachieved.

A fourth embodiment of the present invention which provides onlyfluorescent imaging is illustrated in FIGS. 11-14.

As shown in FIG. 11, the fluorescent imaging device 100 comprises alight source 101, an endoscope 102, an imaging subsystem or camera 103,an image processing subsystem 104, a monitor 105, and a color referencesubsystem 106.

Light source 101 includes a lamp 101 a which may be a metal halide lamp,a mercury lamp, or the like to provide a source of white light. A bluefilter 101 b is disposed in the optical paths of lamp 101 a to generatean excitation light within the blue region, for example between about400 nm and 450 nm.

Endoscope 102 has a slender insertion part 102 a which is designed forinsertion into the organism being examined, and an illumination systemcomprising a light guide 107 a which transfers the excitation light fromlight source 101 to an illumination window 107 b at the tip of insertionpart 102 a. Endoscope 102 also includes an observation optical systemcomprising an observation window 108 a which couples a fluorescent imagefrom the tissue under examination to an image guide 108 b.

Image guide 108 terminates in an eyepiece section 102 a. A lens 108 cfocuses the light output of light guide 108 b for visual observation, orconnection to camera 103.

Camera 103 is removably connected to eyepiece 102 b. Camera 103 includesa dichroic mirror 110 which divides the fluorescent image from eyepiecelens 108 c into a transmitted portion 110 a and a reflected portion 110b. A first band pass filter 110 which transmits a wavelength band λ₁ ispositioned to intercept transmitted light portion 110 a from dichroicmirror 110. A second mirror 113 is positioned to intercept reflectedlight portion 110 d and to reflect it in turn through a second band passfilter 112 having wavelength passband λ₂. A first image intensifier 114amplifies the light transmitted by filter 111 and a second imageintensifier 115 amplifies the light transmitted by filter 112. Imageintensifiers 114 and 115 respectively provide outputs to CCD's 116 and117.

Image processing circuit 104 and a color reference subsystem 106 providevisual data for display on monitor 105. Image processing circuit 104converts the red and green image signals generated by CCD's 116 and 117into a fluorescence image display signal. Color reference subsystem 106includes a color reference generator 106 a which generates a colordiscrimination scale display signal and a superimposing circuit 106 b,which combines the fluorescence image display signal and the colordiscrimination scale display signal into a composite video signal fordisplay on monitor 105. The display includes a portion 105 arepresenting the tissue under examination and a color discriminationscale 105 b. As explained below, color discrimination scale 105 bprovides a reference for objective identification of diseased tissues inaccordance with color tone variations in the tissue image display 105 a.

The operation of fluorescent imaging device 100 will now be illustrated.

The excitation light λ₀ within the blue region is generated by lamp 101a of the light source 101 and is then introduced into the light guide107 a of the endoscope 102. The excitation light λ₀ passes through lightguide 107 a and then is emitted through illumination window 107 b towardthe tissue under observation. The fluorescent image stimulated by theexcitation light is transferred through the observation window 108 a andthe image guide 108 b to the eyepiece part 102 b at the operator sideand then is emitted into the camera 103.

The fluorescent image which is emitted into the camera 103 is partiallytransmitted and partially reflected by dichroic mirror 110. Thetransmitted portion 111 a passes through first bandpass filter 111; andafter being amplified at the first image intensifier 114, is imaged atCCD 116 to undergo photoelectric conversion to an electric signal.

The reflected portion 110 b of the fluorescent image is again reflectedby the mirror 113 and then passes through second bandpass filter 112,and after being amplified at the second image intensifier 115, is imagedat CCD 117 to undergo photoelectric conversion to an electric signal.

As will be understood, the electric signals produced by CCDs 116 and 117represent single-color fluorescent light images with different colortones. These are connected into the image processing circuit 104 a whicharithmetically processes the two input signals to generate thefluorescence image display signal.

As shown in FIG. 12, the fluorescence within the visible region which isstimulated by the excitation light shows an intensity distribution in alonger wavelength band than that of the excitation light λ₀ which isemitted from the light source device 101. Normal tissue shows a strongfluorescent intensity within the range near to the green region λ₁,especially of 490 nm through 560 nm, while for abnormal tissue such asthat of cancer or the like, the fluorescent intensity is relativelyweaker in this band. On the hand, the fluorescent intensity of abnormaltissue the red region λ₂, especially within the range of about 620 nmthrough about 800 nm, though attenuated compared to the intensity ofnormal tissue, is attenuated to a much lesser degree relative to normaltissue than in the green band λ₁. Accordingly, it is possible to utilizethe differences in relative intensity between normal and abnormal tissuein the red and green bands to discriminate between and normal andabnormal tissue.

Therefore, the fluorescences which exist near green region λ₁ and redregion λ₂ may be converted by image processing circuit 104 into a singlefluorescence image display signal from which the condition of tissue maybe observed, by viewing the tissue image display 105 a on the screen ofmonitor 105.

To make it easy to discriminate visibly between normal and abnormaltissue, an image of the green region λ₁ is displayed as a cyan videosignal and an image of the red region λ₂ is displayed as a red videosignal.

Then, as shown in FIG. 13, when the tissue image 105 a is displayed onmonitor 105 with cyan and red, normal tissues are visualized as cyan andcancer lesions as dark red. A dysplasia, which is a precancerous lesion,is visualized as a lighter red.

The value of the difference or the ratio of the λ₁ and λ₂ image signalsmay be obtained from image processing circuit 104 as the fluorescenceimage display signal, the color of which corresponds to the value of thedifference or the ratio.

Referring still to FIG. 11, a color reference generator 106 a, which maybe of any conventional or desired design, combines a signal representinga cyan color and a signal representing a red color in various ratios togenerate the color indication signal data representing the colors for acolor discrimination scale 105 b on monitor 105.

In this embodiment, as shown in FIG. 14, the coloration discriminationscale 105 b comprises four distinct bands 200 a-200 d, respectivelyproviding cyan, white, bright red and dark red reference colors. Colordiscrimination scale 105 b is displayed on the monitor 105 bysuperimposing circuit 106 b along with the tissue image 105 a.

Therefore, an operator can make an objective discrimination of subtlecoloration differences in the tissue image display by comparing thecoloration of image 105 a with the color reference bands 200 a-200 d incolor discrimination scale 105 b, and then can diagnose abnormalconditions such as the existence of a lesion, the extent of the lesion,and the like is an objective manner. In other words, a commondiscrimination standard can be provided which is independent ofdifferences between operators and also in facilities such as hospitalsand the like.

Although two single colors are used in this embodiment to form thetissue image 105 a, many single colors may be mixed. Also, the colordiscrimination scale 105 b is not limited to four color reference bands.Therefore, by displaying the tissue image while increasing the number ofcolor reference bands as well as the relative brightness of individualcolors, changes in appearance of the image due to the brightness of thefluorescent image can be confirmed. Moreover, the color discriminationscale 105 b may be moved by means of superimposing circuit 106 b toposition it adjacent to a particular portion of tissue image 105 a (ormay even overlie other parts of image 105 a) which makes colorcomparisons easer and more reliable. This may be done in anyconventional or desired manner, as by use of a scale positioner 205 suchas mouse or other manual input device.

A fifth embodiment of the present invention is illustrated in FIGS.15-17.

As shown in FIG. 15, a fluorescent imaging device 100 a of thisembodiment includes light source 101, an endoscope 102 and a camera 103which are the same as the corresponding components of the fourthembodiment, and an image processing circuit 104 described in detailbelow.

Light source 101 includes, by way of example, a wide-band lamp 101 a anda blue filter 101 b which passes only blue and ultraviolet light tolight guide 107 a in endoscope 102. An illumination window 107 b directsthe excitation light onto the tissue under observation.

A fluorescent image generated in response to the excitation light istransferred through an observation window 108 a and an image guide 108 bin endoscope 102 to an eyepiece 102 b, and is then coupled to camera 103through the eyepiece lens 108 c.

Image processing circuit 104 comprises first and second CCU's 143 and146, respectively coupled to the outputs of first and second CCD's 116and 117 in camera 103. First and second analog to digital (A/D)converters 144 and 147 are respectively connected to the outputs ofCCU's 143 and 146. These, in turn, provide input signals for respectivelookup tables (LUT's) 145 and 148. LUT 145 corrects the output of A/Dconverter 144 in accordance with the response characteristics of I.I.114 and CCD 116 in camera 103, and LUT 148 adjusts the output of A/Dconverter 147 to match the response characteristics of the second I.I.115 and the second CCD 117 in camera 103 to the typical characteristicsof human vision. A video processor 149 generates tissue image displaysignals from the corrected data generated by LUTs 145 and 148 fordisplay on monitor 105.

Image processing circuit 104 computes the maximum values of thebrightness levels of the raw color image signals 152 and 154 provided byCCD's 116 and 117 and adjusts these signals to produce an output videodisplay on monitor 105 in which normal tissue is displayed in apredetermined reference color. This is accomplished by a computationcircuit 141, a control circuit 142, and a color tone adjustment switch150.

Computation circuit 141 computes the frequencies of the brightnesslevels (histograms) of the image signals from LUTS 145 and 148, andcontrol circuit 142 obtains the peak ratios of the distributions of thehistograms for the green and red signals obtained by computation circuit141, and also adjusts and controls the amplification ratios of I.I.s 114and 115 so that the peak ratios are at the frequencies corresponding tothe color tones of normal tissues. Image processing circuit 104 furtherincludes a color tone adjustment switch 150 which initiates the processof adjustment of the amplification ratio.

In operation, camera 103 functions as described in connection with thefourth embodiment to produce image signals on conductors 152 and 154respectively representing the green and red components of thefluorescent image.

The green fluorescent image signal on conductor 152 is processed by thefirst CCU 143 and then is converted into a digital signal by A/Dconverter 144. Then this digital data is corrected to match the responsecharacteristics of human vision by the first LUT 145 where thecorrection data which are fitted to the response characteristics of thefirst I. 114 and the first CCD 116 are recorded.

The red fluorescent image signal appearing on conductor 154 is processedby CCU 146 and then is converted into a digital signal by A/D converter147. This digital data is corrected to match the responsecharacteristics of human vision by the second LUT 148 where thecorrection data which are fitted to the response characteristic of thesecond I.I. 115 and the second CCD 117 are recorded.

The corrected digital signals are used to generate a so-called pseudocolor image signal in video processor 149. This is displayed as an imagerepresenting the tissue under examination on the screen of the monitor105. The color tone of the tissue image corresponds to the ratio of thedigital data for the green and red fluorescent images produced by LUTs145 and 148 respectively. In order words, for a normal tissuecharacterized by a green image component which is larger than the redcomponent, the image is displayed with a cyan color tone, and in thecase of an abnormal tissues such as cancer tissues where the redcomponent is larger than green components, the image is displayed with ared color tone.

However, if the gain or amplification of the second I.I. 115 whichamplifies the red fluorescence is relatively higher than the gain offirst I.I. 114 which amplifies the green fluorescence, normal tissuewill be displayed with a whitish cyan coloration and an abnormal tissuewill be displayed with a much more reddish coloration. On the otherhand, if the gain of second I.I. 115 is much lower than that of firstI.I. 114, normal tissue will be displayed with a much greater cyaniccolor tone and abnormal tissue will be displayed with a darker color.

To calibrate the system so normal tissue is displayed in the desiredcyan color, the operator pushes color tone adjustment switch 150 whileobserving normal tissue.

This automatically starts the color tone adjustment process. In general,the gain of the second I.I. 115 which amplifies the red fluorescence isrelated to the gain of I.I. 114 which amplifies the green fluorescenceaccording to the relationship:

R(G)=aG ² +bG+c  (1)

Here, R is the gain of the second I.I. 115, G is the gain of the firstI.I. 114. The coefficients (a) and (b) and additive term (c) areconstants.

Coefficient (a) corrects for non-linearity of the individual gaincharacteristics of the I.I.s 114 and 115, and coefficient (b) correctsthe relative gains of the I.I.s 114 and 115. Constant term (c) is anoffset value.

By adjusting the value of (b), adjustment of the color tone for normaltissue can be achieved.

To simplify the illustration of the process of the color tone adjustmentwhich is described hereinafter, the values of (a) and (c) are set to be0, i.e. that there is no non-linearity or offset. Referring to FIGS.16A, 16B and 17, to begin the process, color tone adjustment switch 150is pushed as described above during the observation of normal tissues.At Step S1, computation circuit 141 operates control circuit 142 to setthe gain of I.I.'s 114 and 115 to be equal, i.e., b=1 in equation (1).Using these gain values, the green and red fluorescent image signals 152and 154 are processed by CCU's 143 and 146, A/D converters 144 and 147,and LUT's 145 and 148 as described above, and the resulting imagesignals provided by LUT's 145 and 148 are provided to computationcircuit 141. The process then shifts to Step S2.

At Step S2, as shown in FIG. 16A and FIG. 16B, the histograms of the redand green image signals are calculated. The process then shifts to StepS3 where from the histogram of the individual colors, namely those ofred and green, the maximum values for green H_(G) and red H_(R) arecomputed. The process then shifts to Step 4, where the ratioR=(H_(G)/H_(R)) of the maximum value for green, H_(G) and the maximumvalue for red, H_(R) is obtained.

The process then shifts to Step S5 where the value of the ratio R whichis obtained in Step S4 is compared with a first reference value R₁. IfR<R₁ the process shifts to Step S6 where the value of the term b isincreased by, for example 0.1 and the treatment from Step S2 is repeatedagain using LUT values for relative gain represented by b=1.1.Therefore, until R>R₁, the steps from Step S2 to Step S5 are repeatedlyperformed. When the value of the ratio R becomes larger than the R₁, theprocess shifts to Step S7.

Here, the value of R for which R>R₁ is compared to a second referencevalue R₂. If R>R₂, the process shifts to Step S8 where the value of theterm b is reduced by, for example, 0.1, and steps S2-S5 and S7 arerepeated.

The process continues as described until the value of R falls within therange R₂>R>R₁. When this condition is satisfied, the process terminates.

For the above-described computation process it is found that the valuesof R₁ and R₂ should be set to a relatively wide value compared to thechanges in the value by 0.1 in Step S8.

As a result of the above-described enhancement process, normal tissuesare displayed on monitor 105 in an easily recognized cyan color, andabnormal tissues are displayed in an equally recognizable dark red colortone. As a result, an operator can objectively discriminate betweennormal and abnormal tissues and easily identify lesions, cancerous andprecancerous tissues, etc.

FIG. 18 illustrates a sixth embodiment of the present invention which ineffect combines the features of the first and fourth embodiments. Forthis embodiment, camera 4 (not shown) which is identical to that shownin FIG. 1, provides a white image output signal from CCD 40 andfluorescent image output signals from CCDs 51 and 55. These are providedas inputs to control center 5′. This includes CCU for white use 41 whichreceives as its input the white image signal from CCD 40, and imageprocessing circuit 104 a which receives its inputs from CCDs 51 and 55(see FIG. 11). CCU for white use 41 provides an input to switchingarrangement 42, a second input to which is provided by superimposingcircuit 106 b. This in turn receives its inputs from image processingcircuit 104 a, color reference generator 106 a and positioning device205, all of which function in the manner of the correspondingly numberedelements described in connection with FIG. 11.

Control center 5′ also includes a control circuit 8 and a start switch7. Control circuit 8 provides a control output to switching arrangement42 to select whether the white light image provided by CCU for white use41 or the fluorescent image provided by superimposing circuit 106 b iscoupled to a monitor 6. Control circuit 8 receives additional inputs andprovides additional outputs as described in connection with FIG. 1.

FIG. 19 shows a seventh embodiment of the present invention whichessentially combines the features of the first and the fifthembodiments. Here, camera 4 (not shown) and monitor 6 functionessentially in the same manner as described in connection with FIG. 1,and control center 5″ performs a combination of the functions of controlcenter 5 of FIG. 1 and image processing circuit 104 of FIG. 15.

Specifically, control center 5″ includes CCU for white use 41 whichprocesses the white light image signal provided by CCD 40, CCU 143, A/Dconverter 144, and Look Up Table (LUT) 145 which process the green colorband component signal of the fluorescent image, and CCU 146, a/dconverter 147 and LUT 148 which process the red color component signalof the fluorescent image. The outputs of LUTS 145 and 148 are coupled tovideo processor 149. All of these elements function in the same manneras the correspondingly numbered elements described in connection withFIG. 15. Video processor 149 provides a second signal input to switchingarrangement 42. A control signal input for switching arrangement 42 isprovided by control circuit 8 which selects between the white lightvideo signal and the fluorescent light video signal in the mannerdescribed in connection with FIG. 1.

Control center 5″ also includes computation circuit 141, imageintensifier control circuit 142 and calibration start switch 150 all ofwhich function in the manner described with respect to the like numberedelements in FIG. 15.

As previously indicated, the sixth and seventh embodiments respectivelyillustrated in FIGS. 18 and 19 function in the same manner as theembodiment of FIG. 1 to select between display of a white light image ora fluorescent image and to protect the high sensitivity imaging circuitsused to process the fluorescent image color band data. The sixthembodiment operates as described in connection with FIGS. 11 through 14to provide an enhanced fluorescent image display and a color referencedisplay for simultaneous presentation on the monitor, while the seventhembodiment operates in the manner described in connection with FIGS. 15through 17 to provide color and light level correction for the videodisplay of the fluorescent image.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will be apparent to those skilled in the art. It isintended, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claim is:
 1. A fluorescent imaging device capable of imagingboth of a white light and a fluorescent light, comprising: a lightsource for endoscope use which selectively emits a plurality of lightsinclusive of at least white light and fluorescent light; an endoscopewhich comprises a light guide for guiding the lights emitted from saidlight source, for capturing an image obtained by emitting the light ontoan object from said light guide; an imaging camera having at least onewhite light imaging means and at least one fluorescent light imagingmeans each for imaging the image captured by said endoscope; and animage producing means capable of producing a plurality of image signalsfrom an electric signal which corresponds to the light selected amongsaid plurality of lights and which is developed as an output from saidimaging means; a selection means provided in either one of said lightsource, said image producing means and said endoscope for selecting aspecific one among said plurality of lights; a setting means for settingthe specific light selected by said selection means; and an initialsetting means which selects said at least one white light imaging meansprior to the setting by said setting means whereby said at least onefluorescent light imaging means is prevented from receiving light whensaid light source is turned on.
 2. A fluorescent imaging device capableof imaging both of a white light and a fluorescent light, comprising: alight source for endoscope use selectively which emits a plurality oflights inclusive of at least white light and fluorescent light; anendoscope which comprises a light guide for guiding the lights emittedfrom said light source, operative to capture an image obtained byemitting the light onto an object from said light guide; an imagingcamera having at least one white light imaging device and onefluorescent light imaging device each responsive to the image capturedby said endoscope; and an image producing circuit capable of producing aplurality of image signals from an electric signal which corresponds tothe light selected among said plurality of lights and which is developedas an output from said imaging camera: a selection device provided ineither one of said light source, said image producing circuit and saidendoscope operative to select a specific one among said plurality oflights; a setting device for setting the specific light selected by saidselection device; and an initial setting device for selecting said atleast one white light imaging device prior to the setting by saidsetting device whereby said at least one fluorescent light imaging meansis prevented from receiving light when said light source is turned on.3. An endoscope apparatus comprising: a light source device capable ofselectively irradiating an object with a first illumination light of afirst type for conventional observation and a second illumination lightof a second type different from the first type for special observation;an endoscope having an imaging device for conventional observation whichimages an object by the first illumination light and an imaging devicefor special observation which images an object by the secondillumination light; an imaging prevention device which prevents imagingby the imaging device for special observation; and a controller whichcontrols the imaging prevention device so as to prevent imaging by theimaging device for special observation when the light source device isin a transitional state.
 4. An endoscope apparatus according to claim 3,wherein the light source device is capable of being in a transitionalstate when the light source device is turned on.
 5. An endoscopeapparatus according to claim 3, wherein the light source device iscapable of being in a transitional state when the light source device isturned off.
 6. An endoscope apparatus according to claim 3, wherein apower supply for a camera is in a transitional state when switched fromthe first illumination light to the second illumination light, and whenswitched from the second illumination light to the first illuminationlight.
 7. An endoscope apparatus according to claim 3, wherein theimaging prevention device interrupts an optical path of the firstillumination light in order to prevent the first illumination light frombeing incident on the imaging device for special observation.
 8. Anendoscope apparatus according to claim 3, wherein the imaging preventiondevice controls a power source for the imaging device for specialobservation.
 9. An endoscope apparatus according to claim 3, wherein theimaging prevention device controls a sensitivity of the imaging devicefor special observation.
 10. An endoscope apparatus comprising: a lightsource device that can selectively irradiate onto an object a firstillumination light for conventional observation and a secondillumination light for special observation; an endoscope having a firstmode for conventional observation by an imaging device for conventionalobservation that images an object by the first illumination light and asecond mode for special observation by an imaging device for specialobservation which images an object by the second illumination light; animaging prevention device which prevents imaging by the imaging devicefor special observation; and a controller that controls the imagingprevention device so as to prevent imaging by the imaging device forspecial observation until the first mode for conventional observation isestablished when the light source device irradiates the firstillumination light onto the object.
 11. An endoscope apparatus accordingto claim 10, wherein the first mode for conventional observation isestablished when a power supply of the endoscope is turned on.
 12. Anendoscope apparatus according to claim 10, wherein the first mode forconventional observation is established when a power supply of theendoscope is turned off.
 13. An endoscope apparatus according to claim10, wherein the first mode for conventional observation is establishedwhen switching between the mode for conventional observation and themode for special observation.
 14. An endoscope apparatus according toclaim 10, wherein the imaging prevention device interrupts an opticalpath of the first illumination light in order to prevent the firstillumination light from being incident on the imaging device for specialobservation.
 15. An endoscope apparatus according to claim 10, whereinthe imaging prevention device controls a power source for the imagingdevice for special observation.
 16. An endoscope apparatus comprising: alight source device that can selectively irradiate onto an object afirst illumination light for conventional observation and a secondillumination light for special observation; an endoscope having a firstmode for conventional observation by an imaging device for conventionalobservation that images an object by the first illumination light and asecond mode for special observation by an imaging device for specialobservation which images an object by the second illumination light; animaging prevention device which prevents imaging by the imaging devicefor special observation; a controller that controls the imagingprevention device so as to prevent imaging by the imaging device forspecial observation until the first mode for conventional observation isestablished when the light source device irradiates the firstillumination light onto the object; wherein the imaging preventiondevice controls a sensitivity of the imaging device for specialobservation.
 17. An endoscope apparatus comprising: a light sourcedevice which can selectively irradiate onto an object a firstillumination light for conventional observation and a secondillumination light for special observation; an endoscope having a firstimaging device that images an object by the first illumination light anda second imaging device that images an object by the second illuminationlight; an imaging prevention device which prevents imaging by the secondimaging device; a light detecting device which detects the secondillumination light; and a controller that controls the imagingprevention device to prevent imaging by the second imaging device basedon the result of detection by the light detecting device.